T’was the week before Christmas when all through (Wentworth) Woodhouse, BBC crews were stirring with cameras, laptops and even a mouse.

It’s about magic, and magicians

December 18, 2013, to be exact – just outside Rotherham in the sort of country pile that wouldn’t look out of place in an episode of Downton Abbey.

It might seem strange to be talking about two Christmases ago, but then a lot of work went into the production of Jonathan Strange & Mr Norrell, BBC One’s new seven-part series, which finally comes to screens tomorrow.

Back in the winter of 2013, filming was under way, and ‘festive’ wasn’t the only spirit seeping through the set, as the likes of Hustle’s Marc Warren and Eddie Marsan prepare for their close-ups.

A fantasy saga, based on Susanna Clarke’s acclaimed 2004 novel, Jonathan Strange & Mr Norrell, is set in an alternate 19th Century England.

“It’s a fantasy, but really it’s about people, and they’re very sharply drawn people. It’s a grown-up drama.”

The Olivier Award-winner – who helped turn Tim Minchin’s musical version of Matilda into a West End smash, starred in Channel 4’s hit comedy Babylon and, more recently, played Nick Clegg in TV movie Coalition – was weaned on fantasy novels. He says he knows all about the “stigma” that’s sometimes attached to anything that’s “about an imaginative world”.

Of course, there’s a big gulf between the pulp sci-fi stories which attracted that stigma, and the quality fantasy epics of more recent years.

“What’s amazing about this novel, and about this show, is that it’s properly thought through and the characters have real arcs, they’re real people. It’s a fully imagined world in which magic exists, but it’s one that still recognisable human beings inhabit; men who have a talent for magic.

“One believes in their motivations, and that’s really what the drama’s about,” adds the London-born 37-year-old. “Some extraordinary things happen, but the way that people deal with those extraordinary situations is something that you can really believe in.”

His co-star Eddie Marsan, known for his work on Mission: Impossible III, Happy-Go-Lucky and Filth, was thrilled to sign up for such a fantastical project.

“What’s most interesting about the magic is talking with Susanna, the author, about what the magic signifies,” explains the 46-year-old, who plays Mr Norrell. “The story’s basically about letting the genie out of the bottle and trying to get it back in, and the ramifications of that.

“We talked about many things like that. It could be nuclear power or the subconscious – loads of different things. And it’s the beginning of the 19th Century.”

As the talent head to make-up, I take the opportunity to tour the premises, which is buzzing with runners and camera crew.

The set is rather relaxed and Marc Warren stands almost motionless off-camera, his beautifully coiffured hair covered in a hairnet. He plays ‘The Gentleman with the Thistle-Down Hair’, and is eerily reminiscent of Gary Oldman’s foppish Dracula.

Fast-forward to now – with production complete and mere days until the series finally reaches screens – and Samuel West, who also stars in the series, is thrilled by what he’s seen of the finished product.

“I’ve seen the first two episodes, which I have to say were completely excellent,” enthuses the 48-year-old Mr Selfridge star.

“It’s a really jolly role actually; he’s called Walter Pole, and he has the fortunate position of having a beautiful young wife, who then very sadly dies. There’s inevitable money worries, because she brought a lot of money, but more importantly, he’s heartbroken at the loss of this new relationship. So the new man in town, Gilbert Norrell, who needs to make a splash, decides that the way to do it is to raise Lady Pole from the dead.”

Obviously, the actor is keen not to reveal too much, but he’s thrilled by the scale and calibre of the production.

“It’s over seven episodes, so it’s quite a biggie, and it’s got a terrific cast, especially the two leads. There’s a lot of nice CGI, which isn’t gratuitous; it absolutely serves the story. I hope it’s going to be very successful.”

With Benedict Cumberbatch now preparing to take on the role of comic book sorcerer Dr Strange for Marvel Studios (the movie’s due out in 2016), these are strange days indeed for some of Blighty’s most magical thespians.